1. Field of the Invention
The present invention relates to a wireless network system and a network address assigning method and more particularly to the wireless network system and network address assigning method capable of automatically assigning a network address to each of communication units making up a tree- structure-type wireless network system. The present application claims priority of Japanese Patent Application No. 2000-313584 filed on Oct. 13, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
A wireless network system is known in which a plurality of communication units are connected with each other in a wireless manner. In such the wireless network system, a network address determined uniquely in a network is assigned to each of the communication units. When the communication units carry out communications with each other in the network, the communication unit to be operated as a destination unit is identified by the network address.
FIG. 25 shows a known wireless network system in which a plurality of communication units is connected, in a wireless manner, to carry out communications among child terminals of PHSs (Personal Handyphone Systems). As shown in FIG. 2b, a plurality of the communication units is made up of a radio-relay terminating station 101, radio-relay stations 102-1 to 102-5, and wireless terminals 103-1 to 103-4.
The radio-relay terminating station 101 is connected to the radio-relay station 102-1 and to the radio-relay station 102-2. The radio-relay station 102-1 is connected to the radio-relay station 102-3 and to the radio-relay station 102-4. The radio-relay station 102-2 is connected to the radio-relay station 102-5. The radio-relay station 102-3 is connected to the wireless terminal 103-1 and to the wireless terminal 103-2. The radio-relay station 102-4 is connected to the wireless terminal 103-3. The radio-relay station 102-5 is connected to the wireless terminal 103-4.
Such the wireless network system is regarded as a graph in which each of a plurality of the communication units serves as a node and each of connection relations among them serves as a side. The graph is constructed so as to be of a tree structure and a path to connect the radio-relay terminating station 101 to one of the wireless terminal 103-j (j=1,2,3, and 4) is determined uniquely. Of the communication units connected on the path, each of the radio-relay station 102-i (i=1,2) existing on a side of the radio-relay terminating station 101 is defined as a parent station of each of the radio-relay stations 102-i (i=3,4 and 5) and each of the radio-relay station 102-i (i=3,4 and 5) being connected to each of the parent stations is defined as a child station. Of the communication units connected on the path, each of the wireless terminals 103-j existing on the side of the radio-relay terminating station 101 is defined as a parent station of each of the wireless terminals 103-j and each of the wireless terminals 103-j being connected to each or the parent stations is defined as a child station of each of the defined parent stations.
At this point, the wireless terminals 103-j are always child stations of the radio-relay stations 102-i. Each of the radio-relay stations 102-i is the child station of the radio-relay terminating station 101 or each of the radio-relay stations 102-i′(i′≠i) and is the parent station of the radio-relay station 102-i″(i″≠i) or each of the wireless terminals 103-j. The radio-relay terminating station 101 is always the parent station of the radio-relay station 102-i. Though, in the example shown in FIG. 25, the radio-relay terminating station 101 is connected indirectly through the radio-relay station 102-i to the wireless terminal 103-j, the radio-relay terminating station 101 may be connected directly to the wireless terminals 103-j.
For example, the radio-relay terminating station 101 is the parent station of the radio-relay station 102-1 and the radio-relay station 102-1 is the child station of the radio-relay terminating station 101. The radio-relay station 102-1 is the parent station of the radio-relay station 102-3 and the radio-relay station 102-3 is the child station of the radio-relay station 102-1. The radio-relay station 102-3 is the parent station of the wireless terminal 103-1 and the wireless terminal 103-1 is the child station of the radio-relay station 102-3.
The radio-relay terminating station 101 manages data received from the child station in a unified way and transmits data addressed to each of the wireless terminals 103-j to each of the wireless terminals 103-j. The radio-relay terminating station 101, when being not connected directly to the wireless terminals 103-j being a destination unit, hunts any child station (radio-relay station 102-i) being connected to the wireless terminal 103-j and transfers the data to the hunted child station (the radio-relay station 102-i).
The radio-relay station 102-i transfers data received from the child station to the parent station and transmits data addressed to the wireless terminal to the wireless terminal. The radio-relay station 102-i, when being not connected directly to the wireless terminal 103-j being the destination unit, hunts any child station (that is, the radio-relay station 102-i′) being connected to the wireless terminal 103-j and transfers data to the child station (that is, to the radio-relay station 102-i′). The wireless terminal 103-j is movable and, by being the child station of the radio-relay station 102-i or the radio-relay terminating station 101, transmits data to the radio-relay terminating station 101 and receives data addressed to the wireless terminal 103-j.
In the above wireless network system, the radio-relay terminating station 101 has a function of a DHCP (Dynamic Host Configuration Protocol) server as disclosed in Japanese Patent Application Laid-open No. Hei 11-55317 and each of a plurality of communication units in the wireless network system, by carrying out communications with the radio-relay terminating station 101, acquires a network address. At this point, the wireless terminal 103-j, when moving, can change its parent station and the radio-relay terminating station 101, every time the wireless terminal 103-j moves and changes its parent station, reassigns the network address to the wireless terminal 103-j that has moved and changed its parent station.
In that case, communication data gathers in a concentrated manner to the radio-relay station 102-i existing near to the radio-relay terminating unit, which causes traffic in the wireless network system to increase and data transmission efficiency in the entire wireless network system to be reduced. Moreover, when the number of the radio-relay station 102-i to connect the communication unit requesting for the network address with the radio-relay terminating station 101 becomes larger, time required for the relay of data increases more, thus the time necessary to assign the network address increases.
If each of the radio-relay stations 102-i is provided with the function of the DHCP server, it is necessary to assign two or more network addresses for every radio-relay station 102-i. Because of this, when the number of the radio-relay station 102-i becomes larger, work in which the radio-relay terminating station 101 assigns the network address to each of the radio-relay station 102-i increases more.